The present invention relates to coatings, and more particularly to protective coatings and methods of forming such coatings.
A large number of coatings exist for protecting surfaces on a wide variety of industrial and commercial products, many of which present challenges to a satisfactory coated end product. A problem that is common to many applications arises as a result of the flexure or deformation of a coated surface. A protective coating on a surface that is flexible or is subjected to deformation is generally more likely to fail, whether by losing adherence, peeling, cracking, or otherwise exposing some or all of the underlying surface, by wrinkling or buckling, by developing coating areas that are stressed or weakened, and the like. A number of these problems can occur in the relatively new technology of in-mold decoration (IMD). Generally speaking, IMD is the application of text, a pattern, or graphics to a molded part as part of the molding process.
A popular type of IMD process employs the use of insert molding in which a formable film is layered with a protective coating on one side (referred to as the xe2x80x9cfirstxe2x80x9d side or surface), and is printed with text, a pattern, or graphics on an opposite side (referred to as the xe2x80x9csecondxe2x80x9d side or surface). With reference to FIG. 1, which illustrates a conventional IMD process in flowchart form, the film is first printed or xe2x80x9cdecoratedxe2x80x9d with the text, pattern, or graphics in a conventional manner, such as by silk-screening or other types of printing. The film can be decorated on both first and second surfaces, but is commonly decorated on only the surface that is not exposed to wear and the environment (the second surface in many cases). The fact that the text, pattern, or graphics is printed on the opposite (second) side of the film also protects the text, pattern, or graphics from such potentially damaging exposure. Because the film is typically light-transmissive, second-surface decorations will be visible through the film after the product is completed. The first surface is exposed to wear and the environment, and so may need protection from scratches, abrasion, fluids, and the like. Therefore, the first surface is coated with the protective coating. The hardcoat is left uncured so that it can be formed with the film later in the process.
With continued reference to FIG. 1, after the decorations and protective coating have been applied to the surfaces of the film as just described, the film is formed into a desired shape in one of several conventional manners. For example, the film can be vacuum thermoformed, pressure formed, hydroformed, matched metal formed, etc. Considerations in the type of forming operation selected include the amount of film shaping to be performed (referred to as the amount of xe2x80x9cdrawxe2x80x9d needed for the desired final shape, such as a deep draw or shallow draw), and the extent to which the forming operation will damage or affect the protective coating. It is this latter consideration that presents significant problems in conventional IMD processes. Specifically, conventional protective coatings typically need to be cured to achieve their strong and wear-resistant properties. However, once cured, these same properties largely limit the ability of these protective coatings to be stretched, bent, compressed, or otherwise formed without damage. While this is not normally a problem with protective coatings upon a final product, it is a significant problem in the film forming operation described above. Therefore, protective coatings are typically left uncured in conventional IMD processes until after the film forming process.
Although the uncured protective coating can be easily shaped without sustaining damage, it is relatively delicate and susceptible to scratching, marring, impressions, and the like. By way of example only, such damage can occur as the film is being taken out of the printing and coating machinery, when the film is stacked upon other films for transport or otherwise, during movement and handling of the film from the printing and coating machinery to the molding machinery, when the film is inserted into the molding machinery, during the molding operation, when the film is removed from the molding machinery, and during movement and handling of the film from the molding machinery to a location where the protective coating is cured.
In order to protect the uncured protective coatings from damage, special procedures are commonly used, such as restrictions on the amount of film stacking, protection of the film from exposure to light and heat (many protective coatings are cured by exposure to ultraviolet light and/or heat), procedures for particular care in handling the films, and the like. In addition, the ability of many forming operations and machinery to damage the uncured protective coating limits the types of operations and machinery that can be used. The special handling procedures and the inability to employ many types of machinery and processing operations just described represent significant limitations of conventional protective coatings and affects the entire IMD process. These limitations inevitably increase the inefficiency and cost of production of the IMD process and therefore of the end product.
Even with special handling procedures and the use of specific machinery to avoid protective coating damage, the delicate uncured protective coatings inevitably increase the scrap rate of films and the products made with such films. In some cases, even a small number of scrapped films can significantly impact production costs.
Yet another limitation of conventional protective coatings is related to their resulting appearance and performance, and is independent of whether the surface provided with the protective coating is later molded or otherwise shaped. In this regard, it should be noted that conventional protective coatings are commonly applied to a number of different surfaces that are not later molded or otherwise shaped. Although a number of conventional protective coatings are strong and wear resistant, the ability of a manufacturer to control the appearance of the final coated product can often be quite limited. Protective coatings that can be opaque or transparent and that can have a range of glossy, matte, and textured finishes are highly desirable, but are normally not available in one conventional protective coating.
In light of the problems and limitations of the prior art described above, a need exists for a protective coating that can be employed in IMD processes, is strong and wear-resistant, can be cured prior to forming operations of the underlying substrate, is sufficiently flexible and formable after curing to withstand such forming operations without damage, enables the use of a wider variety of molding machinery to form the underlying substrate, reduces the chances of coating damage during substrate printing, handling, transport, and molding processes, reduces scrap rates and production costs, can be transparent or can be partially or fully opaque, and can have a range of finishes (from glossy to matte and a range of textures). Each preferred embodiment of the present invention achieves one or more of these results.
In some preferred embodiments of the present invention, a protective coating is preferably formed as a plurality of dots on a substrate or object which is desired to be protected. As described in greater detail below, the dots can be any shape, can have the same or different shapes, and can be in any density and in any pattern (or no pattern) on the substrate or object. Preferably, the dots are isolated or substantially isolated from one another by uncoated surfaces of the substrate or object, thereby not only providing the substrate or object and the coating with significantly increased cured flexibility and formability, but also with a wide range of possible surface finishes and textures.
Due to the increased flexibility and formability of some embodiments of the protective coating even after being cured, the coated substrate or object can be partially or even fully cured prior to forming operations such as injection molding or film shaping. The substrate or object is therefore less susceptible to damage from handling and from machine operations. This reduces the scrap rate of the substrates or objects being produced and therefore lowers production costs and the cost of the end product. In addition, because the protective coating can be partially or fully cured before forming operations, more types of machines and methods (that could otherwise damage uncured protective coatings) can be employed for forming, shaping, and other manufacturing operations upon the substrate or object being produced.
Although the dots of the protective coating can be applied to a surface in any desired arrangement or pattern, the dots are more preferably applied in an arrangement that is known to present a uniform and pleasing appearance to the protective coating. Most preferably, this arrangement is stochastically generated and is repeatedly reproduced over the surface to be protected. The dots can be any average size, but preferably are an average of between 50 and 150 microns, more preferably are an average of between 80 and 100 microns, and most preferably are approximately 90 microns. The dots can also cover any amount of the surface area to be protected, but preferably cover between 20% and 70% of the surface area, more preferably cover between 20% and 40% of the surface area, and most preferably cover approximately 25% of the surface area.
The protective coating material and the resulting protective coating can be any color desired, but is preferably transparent or substantially transparent. In this manner, the surface beneath the protective coating can be printed or otherwise provided with text or graphics and can have any desired color visible through the protective coating. The protective coating is preferably a second surface protective coating, and can be applied over text or graphics on the first or second surfaces of a film or other object.
Preferably, the protective coating material is an ink that is screen printed upon the surface to be protected. However, other conventional printing and application methods can instead be employed if desired. After being applied to the surface, the protective coating material is preferably cured by exposure to ultraviolet light, although other curing methods are possible (including exposure to air and to heat) depending upon the type of protective coating material used. Once cured, the dots defining the protective coating enable the surface and the protective coating to be flexed and formed without damage, or at least without sufficient protective coating damage to compromise product quality. At the same time, the dots are sufficiently close together to protect the underlying surface from fluids, abrasion, stains, and other damage.
In some highly preferred embodiments, the protective coating can be pre-cured to control the end appearance of the protective coating. In the case of ultraviolet-cured protective coating materials, the protective coating can be initially exposed to relatively low-wattage ultraviolet light. This exposure preferably generates stipple upon the surfaces of the dots defining the protective coating, and can be further enabled by the use of gas flow (e.g., a nitrogen knife) over the dots during exposure to the low-wattage ultraviolet light. Thereafter, the protective coating material can be exposed to higher wattage ultraviolet light to complete the curing process. The amount of stipple can be controlled by (among other factors) controlling the intensity of the low-wattage ultraviolet light, the length of protective coating exposure thereto, and the amount of gas flow over the protective coating.
A surface coated with the protective coating of the present invention can be provided with a much wider variety of final appearances and textures than is possible with conventional protective coatings and coating methods. In particular, the number and pattern (if any) of dots, the average dot size, the amount of surface area covered by the dots, and the type of protective coating material used can all be altered to generate a range of protective coating appearances and textures. An even larger range of appearances and textures are possible by generating and controlling the degree of stipple upon the surfaces of dots as described above.
Further objects and advantages of the present invention, together with the organization and manner of operation thereof, will become apparent from the following detailed description of the invention when taken in conjunction with the accompanying drawings, wherein like elements have like numerals throughout the drawings.